Understanding Period, Group, and Block of Elements in the Periodic Table

Introduction

The periodic table is a fundamental tool in chemistry, organizing elements based on their atomic structure and properties. Elements are categorized into periods, groups, and blocks based on specific rules and characteristics. This article will guide you on how to identify these elements and understand their classification.

Period, Group, and Block Basics

The periodic table organizes elements into a grid where elements share similar properties and atomic structures. These elements can be classified as follows:

Period

A period is the row that an element occupies in the periodic table. Periods 1 through 7 are the rows from top to bottom. Each period corresponds to a different principal quantum number (n), which represents the energy level of the outermost shell. This number of periods increases sequentially as you move down the table.

Group

A group is a column in the periodic table, with a maximum of 18 groups. Most groups are numbered 1 through 18.

Four groups have specific names, which are:

Group 1 (Alkali Metals) Group 2 (Alkaline Earth Metals) Group 17 (Halogens) Group 18 (Noble Gases)

Block

Blocks are named based on the type of subshells (s, p, d, or f) that the valence electrons occupy. Here are the four blocks:

s-block: This includes Groups 1 and 2. p-block: This includes Groups 13 to 18 (except for the aforementioned s-block groups). d-block: This refers to the transition metals, specifically starting from Group 3 and excluding the lanthanides and actinides found in the f-block. f-block: This includes the lanthanides (atomic numbers 57 to 71) and actinides (atomic numbers 89 to 103). It is also referred to as the inner transition metals.

Determining Period and Group

Determining the period and group of an element involves a few steps:

Period

The period of an element is determined by its principal quantum number, which is equal to the row number in the periodic table.

For example, the element with atomic number 15 (Phosphorus) has an electron configuration of 1s2 2s2 2p6 3s2 3p3. The highest principal quantum number (n) is 3, which means it is in Period 3.

Group

The group of an element can be determined by the following rules:

s-block (Groups 1 and 2): The group number is equal to the number of valence electrons. p-block (Groups 13-17): The group number is equal to the sum of the valence electron counts in the ns and np orbitals. d-block (Groups 3-12): The group number is equal to the sum of the valence electron counts in the ns and (n-1)d orbitals, but there are exceptions.

A Practical Method for Determining Period and Group

This method is particularly useful for students aiming to pass the Joint Entrance Examination (JEE), a competitive science exam in India.

To find the period:

Write down the atomic number (Z) of the element. Find the closest upper and lower bounds in the list of noble elements (2101836548611) and locate the period. For example, if Z 38 (Strontium), between 36 (Barium) and 54 (Xenon), the upper bound is 54, and its location is 5. Hence, Period 5.

To find the group:

Subtract the lower bound of the nearest noble element from Z. For Group 1 to 2 elements, if the result (less than or equal to 18), it is the group number. If the result is greater than 18, subtract 14 and use the difference as the group number.

Examples

Let's apply these rules to find the period, group, and block of a few elements:

Example 1: Atomic Number 103 (Lawrencium)

Period: Lower bound 71, Upper bound 86. Since 103 is between 86 (Radon) and 118 (Oganesson), the period is 7. Group: 103 - 86 17, which is Group 17 (Halogens). Block: The last orbital is 7s, so the block is s.

Example 2: Atomic Number 30 (Zinc)

For Period: 28 (Nickel) and 32 (Germanium); since 30 is between 28 and 32, the period is 4. For Group: 30 - 28 2, which is Group 2 (Alkaline Earth Metals). Block: The last orbital is 4s, so the block is s.

Conclusion

Understanding the periodic table and its elements is crucial for any student of chemistry, particularly those preparing for competitive exams. By mastering the rules for identifying periods, groups, and blocks, you can complete your assignments and exams with confidence.

Keywords

periodic table, valence electrons, electron configuration, s-block, p-block